1. Technical Field
The present invention relates to memory devices and methods of manufacturing the same. More particularly, the invention relates to phase change random access memory (PRAM) devices that are configured to efficiently remove residual heat.
2. Related Art
Memory devices can be classified into volatile memory devices or non-volatile memory devices. Volatile memory devices can include random access memory (RAM) devices in which input information is lost if power is shut off. Non-volatile memory devices can include read only memory (ROM) devices in which input information is preserved even if power is shut off. Presently dynamic RAM (DRAM) and a synchronous RAM (SRAM) are often used as RAM devices and flash memory devices are often times used as ROM devices.
DRAMs are advantageous in that power consumption is relatively low and random access is possible. However, DRAMs are volatile and the capacitance of a capacitor in the DRAMs must be increased due to high charge storage capacity. SRAMs are often used as cache memories and are advantageous in that random access is possible and fast operation speeds are also possible. However, SRAM are volatile and their associated manufacturing cost is increased due to a large size of the SRAM. Further, although flash memories are non-volatile, flash memories have a stack structure of two gates, and therefore require higher operating voltages than supply voltage. That is, flash memories require a boosting circuit to generate necessary voltage needed to perform the record and erase operations. Further flash memories may not as easily adapted to be compressed into highly integrated formats and their operating speeds are relatively slow.
In order to address some of these problems associated with memory devices, ferroelectric RAMs (FRAMs), magnetic RAMs (MRAMs) and phase change RAMs (PRAMs) have been developed.
Among these, PRAMs contains phase change material that often times exhibit high resistances in an amorphous solid state and lower resistances in a crystalline ordered solid state. Accordingly, PRAMS can be used to record and read information based on the particular phase the phase change material by exploiting this change in resistance. PRAM promise faster operating speeds and higher integration degree as compared with the flash memory.
Oftentimes PRAMs include a heating electrode for heating the phase change material to drive the phase change of the phase change material. The heating electrode often include a material having a relatively high resistivity to achieve a high heat efficiency under the condition of same electric current, and have a narrow sectional area.
However, after the crystalline state of the phase change material has been initiated by the heating electrode, then residual heat in and around the phase change material remains which can cause thermal and mechanical stresses to the PRAM.
In this regard, the latent heat, which remains after the phase change process, must be removed to improve the electrical reliability of the PRAM.